Field of the Invention
This invention relates to patient interfaces particularly though not solely for use in delivering CP AP therapy to patients suffering from obstructive sleep apnoea (OSA). In particular, this invention relates to cushions used to support and seal the mask to a patient's face.
Description of the Related Art
In the art of respiration devices, there are well known variety of respiratory masks which cover the nose and/or mouth of a human patient in order to provide a continuous seal around the nasal and/or oral areas of the face such that gas may be provided at positive pressure within the mask for consumption by the patient. The uses for such masks range from high altitude breathing (i.e., aviation applications) to mining and fire fighting applications, to various medical diagnostic and therapeutic applications.
One requisite of such respiratory masks has been that they provide an effective seal against the patient's face to prevent leakage of the gas being supplied. Commonly, in prior mask configurations, a good mask-to-face seal has been attained in many instances only with considerable discomfort for-the patient. This problem is most crucial in those applications, especially medical applications, which require the patient to wear such a mask continuously for hours or perhaps even days. In such situations, the patient will not tolerate the mask for long durations and optimum therapeutic or diagnostic objectives thus will not be achieved, or will be achieved with great difficulty and considerable patient discomfort.
U.S. Pat. No. 5,243,971 and U.S. Pat. No. 6,112,746 are examples of prior art attempts to improve the mask system U.S. Pat. No. 5,570,689 and PCT publication No. WO 00/78384 are examples of attempts to improve the forehead rest.
U.S. Pat. No. 6,634,358 and U.S. Pat. No. 6,581,602 of ResMed Limited disclose a nasal mask cushion to sealingly connect a mask to a wearer's face. The cushion has a nose-receiving cavity bounded by a frame and membrane. The membrane is spaced away from the rim of the frame, and its outer surface is of substantially the same shape as the rim.
In the prior art mask cushions are provided that have a solid inner wall that provides support but doesn't allow much change in the shape of the cushion. Thus, such mask cushions can be uncomfortable for a user. Furthermore, often prior art mask cushions are made of foam which is neither waterproof nor durable.